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ESCA Guideline No.6
The Proximity of Offshore Renewable Energy Installations &
Subsea Cable Infrastructures
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Document history
Any party wishing to propose a change to this document should address the proposed change
to the Chair of the Renewables and Power Cables (RPSG) Subgroup of The European Subsea
Cables Association (ESCA). The RPSG will then review the proposed change and consider reconvening the Technical Working Group ("TWG") to discuss the proposal. Once the RPSG (and
TWG, if appropriate) are satisfied, their findings and the revised document will be presented
to the ESCA Plenary and other respective bodies for approval. Only when all parties have
approved the changes will the document be re-issued.
This document is the result of a successful collaborative exercise involving a wide range of
industry and Stakeholder representatives. It is the product of a best practice approach to
minimising the prospect of future disputes whilst maximising seabed development through
the adoption of the principle of sharing the seabed in a manner that is both safe and
sustainable.
The authors would like to thank Department of Energy Security and Net Zero (DESNZ –
Formerly DECC and BEIS), Department of Science Innovation and Technology (DSIT – formerly
DCMS), the Marine Management Organisation (MMO), Marine Scotland, ORE Catapult –
Floating Offshore Wind Centre of Excellence, and OFGEM for their support in the process
leading to the generation of this document.
Disclaimer
The information contained in this document has been compiled by the Renewables Power Sub-Group
("RPSG") of ESCA.
This document is based upon the contributed combined experience and knowledge of the subsea
telecommunication cable industry, the offshore renewable energy industry, the offshore power
transmission industry, The Crown Estate and Crown Estate Scotland. It is published in good faith with the
aims of promoting the highest standards of construction, operability, reliability, maintainability and safety
in the subsea cable environment.
Whilst we reasonably believe the information contained herein to be valid, it is up to those who may seek
to rely on such information to satisfy themselves as to its accuracy. ESCA and all the other named
associations and entities responsible for the information contained in this document and its compilation
make no warranties as to its accuracy and can accept no liability (direct or indirect) for any errors in the
information or for any losses or other adverse consequences arising from its adoption.
It is the intention of this document to give guidance and to facilitate discussions between effected parties,
but it is not intended to replace such discussions, nor is it intended to require any affected party to behave
in a certain way or remove the right of any such party to take its own commercial decisions in relation to
any of the issues raised in this document.
Table 1 Revision Log
Issue No.
Name
1
RPSG
2
RPSG
3
RPSG
4
RPSG
5
Secretary
6
RPSG
Comments
Initial Issue
Revision to format
Interim revision
Major revision
Rebranding to ESCA
Update to include floating wind
Issued & Owned By: Executive Committee
Issue No: 6
Date: 23rd November 2023
Date
Oct 2003
Sept 2006
Sept 2010
Aug 2012
Mar 2016
July 2023
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Table of contents
1
DEFINITIONS & ABBREVIATIONS....................................................................... 4
2
EXECUTIVE SUMMARY ..................................................................................... 6
3
SCOPE OF THE GUIDELINE................................................................................. 7
4
INTRODUCTION ................................................................................................ 9
5
STAKEHOLDER CONSULTATION ...................................................................... 10
6
PROCESS FOR DETERMINING SITE SPECIFIC PROXIMITY DISTANCES................ 11
7
PROXIMITY AGREEMENT ................................................................................ 19
8
MULTIPLE CABLE CROSSINGS IN CLOSE PROXIMITY ........................................ 22
9
DISPUTE RESOLUTION PROCESS ..................................................................... 24
10
RECOMMENDED CONSIDERATIONS, GUIDELINES AND REFERENCES ............... 26
11
ANNEX A - KEY FACTORS DETERMINING PROXIMITY DISTANCES .................... 27
12
ANNEX B STAKEHOLDER CONSULTATION ....................................................... 36
13
ANNEX C – CHECK LIST FOR ISSUES TO BE CONSIDERED IN A SITE SPECIFIC RISK
ASSESSMENT .................................................................................................. 40
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1 DEFINITIONS & ABBREVIATIONS
ALARP - As Low As Reasonably Practicable
BSH (Germany) - Bundesamt für Seeschifffahrt und Hydrographie
CES – Crown Estate Scotland
COLREGS – Convention on International Regulations for Preventing Collisions at Sea, London
20 October 1972, (as enacted in the UK by The Merchant Shipping (Distress Signals and
Prevention of Collisions) Regulations 1996
DAERA - Department of Agriculture and Rural Development of Northern Ireland
DESNZ (UK) – Department of Energy Security and Net Zero
Developer - An entity undertaking a marine development
DOW – Depth Of Water
DP – Dynamic Positioning
DPO – Dynamic Positioning Operator
DSIT (UK) – Department of Science, Innovation and Technology
Dynamic Cable – A cable which has been designed to withstand motion and mechanical
loadings. They are more flexible than standard subsea cables and often used in FOWF’s, sitting
in the water column between the floating WTG’s and the seabed.
ESCA – European Subsea Cables Association
FWTG – Floating Wind Turbine Generator
Hazard Area – An area centred around the vessel and an individual OREI structure adjacent
to a subsea cable, which reflects the OREI structure’s status as a hazard for any vessel
operating on said cable. The radius of the Hazard Area shall be agreed based on the level of
risk to the vessel and the vessel’s own capability.
HSE – Health and Safety Executive
ICPC – International Cable Protection Committee
ISM – International Safety Management
LARS – Launch and Recovery System
MARA (Ireland) – Maritime Area Regulatory Authority
MD – Marine Directorate (Scotland)
MMO – Marine Management Organisation (England)
NM – Nautical Mile (1.852 km)
NRW – Natural Resources Wales
O&M – Operations and Maintenance
OFGEM – Office of Gas and Electricity Markets (Great Britain)
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OREI – Offshore Renewable Energy Installation
OWF – Offshore Wind Farm or Floating Offshore Wind Farms including associated structures
such as foundations, Met Masts, mooring systems and its seabed anchors, subsea cables,
substations etc
UK REA – United Kingdom Renewable Energy Association
ROV - Remotely Operated Vehicle
RUK – Renewable UK
SOLAS - International Convention for the Safety of Life at Sea (SOLAS), 1974
SIMOPS – Simultaneous Operations Procedures
Stakeholder - An entity who is a seabed user or a party with vested interest within the
offshore renewable energy project country
Subsea Cable - An underwater telecommunication or power cable also known as a submarine
cable.
TCE - The Crown Estate.
TWG – cross sector Technical Working Group
UNCLOS - United Nations Convention on the Law of the Sea
Wet Plant – Subsea cables equipment, e.g. repeaters and branching units for subsea
telecommunications cables, or cable joints kits in general for telco and power subsea cables.
Working Zone - The space required either side of a cable by a vessel to conduct all operations
for a cable repair
WTG – Wind Turbine Generator
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2 EXECUTIVE SUMMARY
This document (referred to as the "Guidelines") provides guidance on the considerations that
should be given by all Stakeholders in the development of projects requiring proximity
agreements between OWF projects and subsea cable projects. The Guidelines address
installation and maintenance constraints related to OWF structures, associated cables and
other subsea cables, where such structures and subsea cables will occupy proximate areas of
seabed.
The importance of early Stakeholder engagement should be appreciated at the outset, and
it is recommended that this is actioned as early as possible as described in section 5 and
further expanded in Annex B. The location of existing seabed infrastructure within potential
project development areas could have a significant impact upon the layout or location of a
project and its design. Active communication and Stakeholder engagement are considered to
be the cornerstones of generating the greatest opportunities for a successful outcome.
The Guidelines provide direction in section 6 on a process for determining site specific
proximity distances including factors to consider within risk assessments that may be used to
help inform proximity discussions and agreements. A checklist of key issues is included in
Annex C. The Guidelines also propose some basic principles to form the foundation of
discussions on safe and appropriate solutions on a case-by-case basis, including potential
mitigation measures.
The Guidelines discuss in section 6.1 some of the key factors determining proximity distances
to be taken into account in reaching a proximity and crossing agreement. Further details are
provided in Annex A.
The Guidelines are not intended to provide a prescriptive solution on proximity but, in section
6.2, offer some guidance for indicative proximity distances that are intended as a starting
point for Stakeholder discussions.
Once the parties have agreed site-specific proximity distances, the final step in the process is
the drafting of a proximity agreement with accompanying method statement. Section 7
provides guidance on this topic.
The Guidelines also contain guidance in section 8 on how to deal with multiple cable crossings
in close proximity. Depending upon site specific layout, this may need specific attention,
particularly with the increasing size of OWF’s.
It is expected that the Guidelines will provide the underlying basis upon which all Stakeholders
can reach a mutually acceptable proximity agreement. In the event that proximity discussions
falter, an ultimate recourse in the form of a dispute resolution process is outlined in section
9.
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3 SCOPE OF THE GUIDELINE
The scope of the Guidelines, with respect to the proximity distances and water depths that
they should be applied to, is summarised in Figure 1 below and the following text.
Proximity distances
Figure 1: Proximity distances considered in the Guidelines
The OWF Infrastructure Zone includes as per the OWF definition the associated structures
such as foundations, Met Masts, mooring systems and its seabed anchors, subsea cables,
substations etc.
The spacing (d) distance is calculated at the planning stage taking in consideration the closest
of the OWF structure outer edge limit to the third-party cable outer perimeter.
The proximity distance or distances, are the final distances between the OWF structure outer
edge limit to the third-party cable outer perimeter as agreed between the applicable
Stakeholders (usually the OWF Developer or operator, and the third-party cable owner).
The document makes reference to UK regulatory frameworks however the technical
principles are intended to be applicable across other regions and geographic areas. Other
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requirements arising from other European regulatory frameworks will be added to this
Guideline as an appendix and external feedback is welcome from across Europe.
It is the consideration of the Guidelines that no proximity agreement is required where the
spacing (d) distance between a planned subsea development and planned/existing subsea
infrastructure exceeds one nautical mile (1 NM - 1.852 km) and is higher than three times
DOW.
For a planned subsea development where spacing (d) distance is within 1 NM or is lower
than three times DOW, dialogue needs to be established between the Stakeholders and the
consideration of the Guidelines should apply to establish mutually acceptable proximity
distances.
As an example the indicative proximity distance of 750 m for a DOW under 75 m, or the
indicative proximity having in consideration the largest of 750 m or three times DOW for
deeper water, is not intended to provide a prescriptive solution on proximity but should be
used as a sensible base case to begin Stakeholder discussions to determine actual, case
specific proximity distances. Multiple adjacent crossings between cables in proximity of the
OWF should be considered as being a single entity with associated potential seabed
sterilisation in the proximity discussions risk assessment .
Water depths
For the purpose of the Guidelines the proximity impacts between renewable energy
installations and subsea cables were considered in a range of water depths up to 75m for
fixed structures, but for floating wind developments water depths up to 1,500m. As new
technologies in terms of OWF structures occur it will require a re-appraisal of the issues
assessed here and are therefore beyond the scope of Guideline No.6.
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4 INTRODUCTION
The ongoing development of OWF’s (fixed and floating) has resulted in the need for cross
industry endorsed guidelines on the proximity of subsea cables and OWF. Other forms of
Offshore Renewable Energy Installations (OREI) currently being developed, such as tidal and
wave energy, may also be in close proximity to existing seabed infrastructure. These
Guidelines however focus solely on proximity between the various OWF structures and
subsea cables.
There are common interests between OWF Developers/owners and cable owners regarding
safety, access and maintenance and there is a necessity for the parties to spatially interact in
terms of access to the seabed. The increased use of the seabed for renewable energy
developments, and the potential for multiple uses of the seabed must be appreciated.
The primary common interests of the parties are summarised in Figure 2 below:
Unfettered
WTG array
layout
Figure 2: Primary common interests
The information supplied in this Guideline has been compiled by a cross-sector Technical
Working Group (TWG) comprising members of ESCA, The Crown Estate, Crown Estate
Scotland and Stakeholders from the offshore telecommunications and renewable energy
industries.
The Guidelines are therefore based upon the combined broad experience and knowledge
base contained within the subsea cable industry, the offshore renewable energy industry and
seabed managers (TCE and CES).
Subject to the disclaimer on the cover page of this document, it is the intention that the
Guidelines should be used as a reference document on the subject matter with the aims of
promoting the highest standards of construction, operability, reliability, maintainability and
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safety in the offshore renewable energy and subsea cable environment commensurate with
co-existence in close proximity to each other.
It is very important to appreciate that the Guidelines do not provide a prescriptive solution
on proximity. The distances contained within this document are intended to provide a starting
point for Stakeholder discussions. It is recognised that an OWF Developer may generally
prefer to locate structures closer to existing seabed infrastructure than the Guidelines
indicate. Under certain conditions and layouts this may well be possible.
The optimised proximity distance will only be achieved by dialogue and agreement between
the parties based upon a risk assessment process where appropriate.
It is in the interest of all Stakeholders that to achieve a mutually acceptable and optimal
proximity agreement, very skilled and experienced resources should be utilised during these
discussions. It is of the utmost importance that all Stakeholders understand and appreciate
each other’s requirements and safety issues. All parties should therefore commence
proximity discussions as early as possible, proactively and with open minds.
Evidence based study
To support the development of the proximity guideline The Crown Estate commissioned an
evidentiary desktop (and interview) study in September 2011 (The Crown Estate, 2012).
The study report can be found on the website of The Crown Estate link below:
https://www.thecrownestate.co.uk/media/1764/submarine-cables-and-offshorerenewable-energy-installations-proximity-study.pdf
The evidentiary study is not intended as a guideline document in its own right but is provided
as a reference tool for the parties.
5 STAKEHOLDER CONSULTATION
It is vital that all sectors engage with each other at as early a stage as possible in the
development process, regardless of which sector the Developer is from and who owns the
existing infrastructure. This engagement will facilitate appropriate proximity agreements and
should continue throughout the consenting process and through the operational lifetime of
the asset as illustrated in the below project cycle overview, Figure 3.
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Figure 3: Stakeholder consultation in all phases of the project lifecycle
There is significant growth in OWFs at the present time and hence much discussion herein
assumes that the new development is an OWF (and the existing infrastructure being a subsea
cable). It should be accepted that the Guidelines apply equally if the new development is a
subsea cable and the existing infrastructure is an OWF.
Stakeholder engagement should commence as soon as is practicable following the award of
a development zone or project area and continue with all Stakeholders, throughout the
commissioning process, the project lifetime and until it is fully decommissioned, where
interactions are taking place between and near to other assets.
Please refer to Annex B for further details on proposed Stakeholder consultation.
6 PROCESS FOR DETERMINING SITE SPECIFIC
PROXIMITY DISTANCES
A generic set of limiting distances cannot be derived for all cable/wind farm proximity
scenarios without a large number of caveats and exceptions. The recommended approach is
to use the principles of a holistic risk based process for determining site specific proximity
distances. This allows consideration of a range of external influences, both those beyond the
control of the parties and those internal influences that can be affected by the parties.
Once the parties have agreed site-specific proximity distances, the final step in the process is
the drafting of a proximity agreement with accompanying method statements.
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The overall process is outlined in Figure 4 below:
Process for determining site specific proximity distances
Site specific proximity distances
Use of proximity agreement
wording
Technical and commercial
agreement on proximity distances
for a given site
Figure 4 - Process for determining site-specific proximity distances and drafting a proximity
agreement
Risk to personnel and the influence of HSE legislation and regulation is considered to be
included under external influences in the diagram above (Figure 4), as well as risks included
in operational standards under internal influences.
Personnel risk is properly governed by detailed legislation and is therefore outside the scope
of the Guidelines. However, it should be noted that Safety Of Life At Sea (SOLAS) is one of the
primary drivers for adopting sensible proximity agreements and serves to underpin every
decision process for either risk assessment or mitigation selection and application.
Risk assessment
In order to come to a site-specific agreement between the involved parties it will usually be
necessary to undertake a risk assessment during discussions on proximity agreements. This is
achieved by applying the cyclic approach embedded in the process, as illustrated in Figure 4.
The risk assessment should include an analysis of all relevant site-specific influences (external
and internal), examples of which are given above. In order to provide a sensible basis for
discussion, risks need to be assessed realistically.
Safe separation is required between existing subsea cables, WTG and other OWF structures
to ensure the continuance of reasonable, timely and cost-effective availability to maintain
both the existing and the newly installed assets. The requirements of each Stakeholder are
however likely to vary depending on the site-specific circumstances.
In order for the involved parties to reach agreement it will be necessary to determine the As
Low As Reasonably Practicable ("ALARP") risk level that is acceptable to each Stakeholder.
This will be site-specific and the appetite for risk is likely to vary. The various site-specific
issues should be carefully analysed in respect of risk impact, and a mutually acceptable ALARP
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level of risk agreed. Consideration of the acceptable risks will then allow informed discussions
on the potential mitigations and lead to site-specific proximity distances.
It should be appreciated from the outset by all parties that no activity is ever entirely free
from risk. Companies and regulators do however require that safety risks are reduced to levels
that are ALARP. The technique associated with this often encompasses the use of a risk
severity analysis to try to quantify the issues.
Please refer to Annex C Section 13.3 for details of ALARP principals and a risk severity analysis
Potential mitigation measures to support reaching agreement
Before decisions are made regarding proximity and cable crossings, other solutions should be
considered to potentially mitigate or reduce the impact. Such mitigation measures may
influence a proximity agreement. Examples of potential mitigation measures include:
Ø Diverting the existing cable around an OWF rather than through
it;
Ø Consider the option of undertaking a cable repair on the OWF
limits and lay through the OWF area. For this provision of
additional spare cable for stock and other Wet Plant in case of
repair;
Ø Change the cable repair vessel to a vessel with higher DP
capabilities within the maintenance agreement and the
necessary financial considerations;
Ø Joint use of cable repair vessels in a specific / generic
maintenance agreement;
Ø Construction of an OWF in a different area or reconfiguring the
OWF layout;
Ø If multiple crossings are unavoidable, discussions of the required
number, location and spacing should take place and be agreed;
Ø Undertake appropriate surveys to identify exact location of “in
service” and “out of service” cables (including burial depth or
any associated cable protection solution) as required;
Ø Utilisation of acoustic sensing to monitor risk in cable crossing
areas;
Ø Agreement on site-specific methodologies for repair; and
Ø Methods of arresting any loss of vessel position, e.g., emergency
anchoring procedures, support vessels, etc.
This list is not exhaustive and, depending upon circumstances, additional mitigations could
also be developed by the parties through mutually acceptable operational (and other)
procedures involving OWF Developer / operator / owner and the existing cable owner /
marine repair contractor etc.
The benefits of “safe havens” and “escape corridors” within large OWF’s as potential
mitigations of risk were considered by the TWG. The consensus of discussions with cable
maintenance providers was that such measures do not deliver appreciable mitigation.
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Principal mitigation considerations for gross de-confliction
Following consideration of the issues of proximity and safe operation of co-located subsea
infrastructure, it is apparent that the presence of an OWF development will restrict or prevent
development opportunities for new Subsea Cables through OWFs without both parties
compromising respective systems protection, security and performance objectives. Such
compromise may be either unacceptable or undesirable. Options for mitigation can therefore
become constrained.
Some examples of potential mitigation measures in this instance include:
Ø Routing a new subsea cable through an existing corridor through
an OWF by virtue of a pre-existing subsea cable or designated
cable corridor;
Ø Design crossing agreement within the OWF;
Ø OWF revising the proposed layout;
Ø Route new subsea cables around OWF developments, between
projects or through wind recovery areas where suitable corridors
may exist; and
Ø Subsea cable developers select alternative routes away from
OWFs.
6.1 KEY FACTORS DETERMINING PROXIMITY
DISTANCES
Subsea cables suffer faults primarily due to external aggression and human activities.
Therefore the need to undertake a repair to restore a system quickly and without impediment
is critical to the resilience of vital infrastructure. Stakeholders in discussion on proximity
distances between subsea cables and OWF structures are advised to develop and agree safe
and appropriate solutions on a case-by-case basis to determine how much sea-room is
required to execute a cable repair efficiently and safely.
The subsea cable industry operates in accordance with a generally recognised set of
maintenance and repair processes and procedures. In order to assist all sectors in
understanding the interactions and impacts, six key determinants of sea-room required by a
cable ship are:
Ø
Ø
Ø
Ø
Ø
Ø
Fault location;
Cable recovery methodology;
Cable repair methodology;
Re-deployment;
Burial/cable protection solution, and
Third party assets location
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6.2 GUIDANCE FOR INDICATIVE PROXIMITY DISTANCES
This Guideline does not provide a prescriptive solution on proximity, rather, it stresses the
need for proactive dialogue about a site specific, risk-based outcome. Guidance for indicative
proximity distances is outlined here to provide a baseline for Stakeholder engagement.
Two primary issues to be observed when considering separation from third party vessels are:
Cable maintenance vessel safety zone – The safety zone around the vessel with restricted
manoeuvring ability (maintenance or repair vessel), from approach of other vessels, shall be
established in line with COLREGS 1972. It is also normally requested by the vessel master (in
accordance with Article V of the Convention for the Protection of Submarine Telegraph
Cables, 1884), for all ships to keep at least 1NM clear whilst they are engaged in cable
operations that restrict their ability to manoeuvre. This proximity distance is even more
important in deep water.
Wind farm structure safety zone – Wind farm operators can request, via the Electricity
(Offshore Generating Stations) (Safety Zones) (Application Procedures and Control of Access)
Regulations 2007 (SI/2007/1948), that typically a 50 m safety zone be established around any
wind farm structure when it is fixed to the seabed, however when dealing with floating
offshore wind structures additional consideration needs to be taken concerning horizontal
surface movement and mooring system footprint, including any interference with the
Dynamic Cable. If the Dynamic Cable is in very deep waters and a 'W-shape' configuration is
used, the proximity of this cable to vessels will also need additional consideration as the entire
cable is buoyant in the water. Guidance for the implementation of such safety zones is
provided by the UK DESNZ (Department for Energy Security and Net Zero (DESNZ, 2011
(Revised))1.
Two fundamental concepts must be considered when deriving a generic proximity distance:
Ø Working Zone, applied either side of the subsea cable; and
Ø Hazard Area, applied around the cable repair vessel.
The Working Zone and Hazard Area concepts are further discussed below and can be found
illustrated later in Figures 5, 6 , 7 and 8. These showing how the Working Zone and Hazard
Area would be applied to a subsea cable repair vessel in various scenarios.
Working Zone - A Working Zone is required either side of an in-service subsea cable to enable
access for cable maintenance and repair operations by a suitable vessel. Please see figure 5.
The parameters of the Working Zone are a function of many variables, several being sitespecific. Nevertheless, the Working Zone is the space required by a vessel to conduct all
operations which a cable repair potentially comprises, including those discussed in detail
within Annex A.
1
https://www.gov.uk/government/publications/offshore-renewables-energy-installations-applying-for-safetyzones
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Figure 5: Example of indicative distances required when conducting traditional cable
recovery methods with grapnels in 50 m DOW.
Definition of 'layback’ and 'run on length’ is provided in page 29.
The Working Zone for traditional repair scenarios up to 75 m water depths is likely to be in
the order of 500 m either side of the existing subsea cable. This is based on the expected
area required to undertake cable fault location using trailed electrodes, grapnel and final
bight deployment operations. Greater detail can be found in The Crown Estate Evidentiary
Study.
For water depths beyond 75 m the proximity distances shall follow the parameters resulting
from the working zone calculation.
Consideration should also be given, but not limited to, the following:
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Proximity of other adjacent developments (i.e. oil and gas);
Water depth;
Proximity of hazards, density of traffic and navigation schemes;
Type, size and manoeuvrability of cable repair vessels;
Support vessels;
Cable type and existing burial status/protection;
Alternative repair options, such as a lay-through repair, or
adjusted final bight location;
Predicted prevailing metocean conditions (wind, wave, current,
tides) etc;
Visibility on the seabed for ROV operations;
Seabed type, features, geology and environmental constraints;
and
Proximity to any infrastructure in the water column (e.g. FOWs
mooring systems and Dynamic Cables).
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Nothing in the Guidelines is intended to detract from the Master’s responsibility for the safe
navigation of the vessel and the safety of those on board. The Master will always retain the
prerogative to depart from the Guidelines, or any subsequent plan or agreement reached as
a result of the Guidelines, if circumstances dictate (Ref. Annex A, Section 13.9).
Hazard Area - Independent of, and in addition to, the Working Zone, where there are fixed
structures near to a vessel undertaking cable operations close to the limit of the expected or
planned Working Zone, a Hazard Area should be considered as a trigger radius around the
vessel. If there is potential for a WTG and its substructure to come within this Hazard Area as
a result of vessel movement, then additional risk assessment needs to be carried out and
determination made on the need for application of any appropriate pre-planned risk
mitigations. Where this situation occurs, additional consideration needs to be given to
supplementary control protocols, weather considerations, etc.
The radius of the Hazard Area needs to be determined by discussion between the key
Stakeholders (e.g. OWF Developer, the existing subsea infrastructure owner and any affected
maintenance provider). The Hazard Area should provide sea-room to ameliorate risks of work
in close proximity to a WTG and its substructure (including mooring system and WTG blades).
If there is no other direction for opening that discussion, then it is recommended that
consideration begins at a minimum of 250 m from the OWF outer edge (including
substructure) or rotor diameter if higher. Even at this minimum distance, there will still be
constraints on vessel operations including, but not limited to, repair procedures and weather
criteria.
Figure 6 shows how the Working Zone and Hazard Area would be applied to a subsea cable
repair vessel when operating on the cable line, i.e. during jointing, ROV burial/fault location,
or stock cable laying.
Figure 6: Vessel operation on the cable line
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Figure 7 illustrates how the Hazard Area would be applied to a subsea cable repair vessel
when operating at the extent of the Working Zone. This being when deploying a final bight
between the adjacent WTGs thus presenting a reduced risk solution.
Figure 7: Vessel operation on the extent of the Working Zone when deploying a final bight
Figure 8 illustrates how the Hazard Area would be applied to a subsea cable repair vessel
when driving away from the cable line during a grapnel drive to recover the cable. Note that
the adjacent WTG represents a significant risk should there be any loss in vessel position. An
option to reduce the risk of this occurrence is to plan drives between WTG’s.
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Figure 8: Vessel operation when driving away from the cable line during a grapnel drive to
recover the cable
For detail please refer to Annex A.
7 PROXIMITY AGREEMENT
When site-specific proximity distances have been agreed, a bilateral proximity agreement
with accompanying method statement can then be drafted based on this Guideline. Such a
proximity agreement should be based on the format and spirit of existing cable crossing and
proximity agreements in common use throughout both industries, where appropriate.
It is recommended that where possible, finalisation of OWF layout planning should not be
undertaken until such time as proximity agreements and the requirements therein have been
properly reviewed, discussed and agreed at least in principle, with the OWF Developer, the
cable owner and any affected maintenance providers.
Survivability of agreements is essential to the parties’ interests.
Proximity
agreement
Technical and commercial
agreement on proximity
distances for a given site
t wording
Figure 9: The drafting of a site-specific proximity agreement and Method Statement
7.1 Proximity agreement recommendation
The recommended approach is to use the principle of a bilateral proximity agreement for
each specific scenario.
It is recommended that the following key elements are included in such a proximity
agreement:
Ø Clauses to define the liabilities and rights of both parties;
Ø The exclusion/inclusion of consequential losses;
Ø Details of financial compensation arrangements for each party
where applicable relating to specific arrangements;
Ø Clearly defined limits of the area to which the proximity
agreement applies;
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Ø Details of how the work would be carried out, to include method
statements provided by the party carrying out the work and
accepted by the other party as suitable prior to work proceeding,
it is recommended that installation procedures be included in
the agreement;
Ø Future maintenance requirements of both assets. This should
include the method by which notification of operations by each
party is given to the other and the provision and storage of
additional plant to support agreed repair methodology and the
establishment of local third-party support vessels, if identified as
a requirement;
Ø Definition of the expiry/survival of the agreement (for example,
at the decommissioning and/or recovery of one or other of the
assets); and
Ø Provision of representatives from one party to the other party's
operations and their rights, obligations and limitation of
authority.
When discussing a proximity agreement it is also recommended that Developers consult the
following International Cable Protection Committee (ICPC) Recommendations and relevant
ESCA Guidelines:
Ø ICPC Recommendation No. 2 - Recommended Routing and Coordinating Criteria
for Submarine Telecommunications Cables in Proximity to Other Such Cables2
Ø ICPC Recommendation No. 3 - Criteria to be Applied to Proposed Crossings of
Submarine Cables and/or Pipelines2
7.2 Site specific method statement
A method statement is an essential part of any proximity agreement. The following is a task
checklist which the parties can use as a basis for drafting a site-specific method statement. It
is not intended to be an exhaustive list of items to be included by prescription but should
prompt evaluation of the most useful and relevant issues for consideration.
There needs to be reciprocity with respect to method statements for repairing and installing
across both industries.
Pre requirement for a repair
Ø Delivery of all as-laid positions of infrastructure –, geodetic
datum’s, cable burial, WTG and substructure dimensions
(including moorings and anchors), drawings, as laid coordinates
and blade arc, , WTG and export cables and array cable routes,
in the case of FWTG the Dynamic Cable profile in the water
2
https://www.iscpc.org/publications/recommendations/
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Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
Ø
column, mid-water array cables, crossing constructions, rock
placements, etc.;
Repair procedures (including navigational procedures, SIMOPS,
fault location, cable recovery and repair, post repair inspection
and burial, mattress operations/cable protection);
Emergency 24/7 contact procedures including escalations,
details of any field-specific VHF communication channels and
details of site engineers;
Consideration concerning having a OWF representative aboard
the cable repair vessel;
Historical metocean data on currents and wind to inform marine
providers (may not be available - especially during the O&M
phase);
Requirements when operating during the night;
Establish notification requirements during operations, i.e. daily
reports, notice of seabed interaction, surface vessel activity, etc.
Purchase of additional expendable gear, e.g. additional cable,
crossing materials (should preferably be agreed upon during
early pre-construction discussions);
Establish cable repair vessel requirements;
Establish additional manning requirements, e.g. additional reps,
marine warranty surveyors, anchor watch crews, etc.; and
Establish bridging documents, as appropriate.
Pre-repair
Ø Consider installation of local position reference systems;
Ø Consider temporary cessation of interruptible works nearby;
Ø Establish preferred subcontractors in area for guard boats, tugs,
other support vessels;
Ø Confirmation that WTG’s, which are in the area of the cable ship
operations, are stopped and locked in position, preferably ‘Y’
position, as necessary;
Ø Depending on fault nature and location, powering down of
closest inter-array/collector cables, as necessary;
Ø Up to date metocean data;
Ø ‘Live’ metocean data feed from any applicable on-site
equipment to establish weather window for repair (wave rider
buoys only give out present condition - not forecasts);
Ø Distribution list from all parties for notifications during repair
ops;
Ø Boarding requirements of any additional personnel;
Ø DP trials nearby repair site to establish all systems functioning
correctly; and
Ø Coordination meeting and confirmation of communication lines
(shore project management).
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During repair
Ø Daily activity reporting;
Ø Acknowledgement that the cable repair vessel Master has
overall site authority for the safe management of the repair
activity;
Ø Dependent on communication plan within proximity agreement,
notifications when works are expected to be seabed intrusive;
and
Ø Assistance in enforcing 1 NM clearance zone around repair
vessel for other marine traffic (as no requirement yet exists for
an OWF to have marine coordinators during the O&M phase,
there may not be personnel ashore to monitor marine traffic
daily).
Post repair
Ø Sharing of revised infrastructure location data; and
Ø Post repair review meeting/lessons learnt exercise to feedback
improvements to the process or relevant industry contacts.
8 MULTIPLE CABLE CROSSINGS IN CLOSE
PROXIMITY
A standard protocol for subsea cable crossings is well established and can be found detailed
within ICPC recommendations 2 & 3.
Multiple cable crossings in proximity have been undertaken on several occasions and are
therefore not a new scenario. However, ideally, crossings should be kept to a minimum from
the point of view of the existing cable(s).
Multiple crossings within an OWF area, for example a telecommunication cable or power
cable crossing several inter-array power cables as shown on Figure 10 (for illustration of the
issue only) should generally be avoided or mitigated.
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Figure 10: Potential multiple crossings within an OWF (Ref: The Crown Estate)
The amount and frequency of crossings should form part of discussions on crossing/proximity
agreement between the parties.
When crossings exist recovery of the underlying cable between crossings might be unsafe and
impractical. As such, crossings should be considered as being a single entity (when multiple
crossings occur between the same third-party cable and the OWF cables) and subsequently
sterilising that area of seabed and existing cable. Any repair of the crossed cable would involve
cutting either side of these crossings and lay back over the top.
It is appreciated that the development of large OWF’s has created the potential for a high
concentration of crossings by multiple export, collector and/or array cables. This could result
in limiting the available space for cable repair vessels to operate and also pose technical
problems regarding cable recovery/replacement and repair within the crossing area. It is
recommended that the following principles are initially considered:
Ø Multiple crossings of existing cables by export, collector and/or
array cables should be avoided wherever possible;
Ø Where multiple cable crossings are deemed necessary, the
crossing cables should be spaced so that safe, timely and
economical repairs to both the crossing and the crossed cables
can be conducted without prejudice. An alternative, and if there
are several crossings in short distances, the mutualisation of
crossing positions (designing several cables to cross at the same
location), should be considered. In some circumstances this can
improve the ability to access the crossed cable to conduct a
repair and reduce the effective distance of seabed sterilisation
caused by regular spaced multiple crossings.
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Figure 11: Example of mutualisation of crossing positions
The potential impacts of multiple cable crossings should be carefully assessed. This should be
included in the discussions of proximity/crossing agreements. As with all construction work,
there are many different situations that will need to be considered when multiple cable
crossings in close proximity are being discussed. Before cables are laid close to or across
existing cable(s), it is recommended that the parties should consider the following:
Ø When the operation(s) is/are to be carried out;
Ø Which technical method(s) will be used;
Ø Whether a pre-lay survey is required along both the existing
cable(s) and the route of the new cables;
Ø Whether seabed preparation operations will be undertaken;
Ø At what approach distance from the existing cable(s) the
crossing cables can be buried by plough/ROV/other means of
jetting;
Ø If required, what kind of protection should be used between the
cables at the crossing point (polyurethane, concrete/bitumen
mattresses, rock placement etc.) and the thickness of the
separation layer;
Ø In the event of a later repair, which technical methods are to be
used;
Ø How close can an ROV or a grapnel be used to the other party’s
cable(s); and
Ø Confirm who has priority in the case of simultaneous faults.
9 DISPUTE RESOLUTION PROCESS
It is recommended that any dispute arising out of or in connection with the parties'
negotiations to establish an agreed distance between the subsea cable and OWF
Development in question (a dispute) may be resolved by using a typical mediation process
used in the UK; an example of which is shown below:
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In the event of any matter for expert determination, senior representatives of the parties shall,
within [30] calendar days of service of a written notice from any party to the other parties (a
disputes notice), hold a meeting (a dispute meeting) in an effort to resolve the dispute. If the
parties are unable to agree upon a venue, the dispute meeting shall be held at an appropriate
neutral location. Each party shall use all reasonable endeavours to send a representative who
has authority to settle the dispute to attend the dispute meeting.
If the representatives of the parties cannot resolve the dispute within [60] calendar days after
the service of a disputes notice, whether or not a dispute meeting has been held, the dispute
must be referred to a senior manager of UK operations of each party who must use all
reasonable endeavours to resolve the dispute within [30] business days after the dispute is
referred to them (referral period).
Any dispute which is not resolved within the referral period, shall, at the request of any party
made within [30] calendar days of the expiry of the referral period, be referred to an
independent expert for determination.
The parties shall agree on the appointment of the expert and shall agree with the expert the
terms of their appointment. If the parties are unable to agree on the identity of the expert, or
if the person proposed is unable or unwilling to act, then, within [30] calendar days of either
party serving details of a suggested expert on the other or the proposed expert declining to
act, either party shall then be entitled to request that an expert be appointed by an
independent arbiter. All costs of and associated with the request for the appointment of an
expert by the independent arbiter shall be borne equally between the parties. The expert
appointed may be an individual, partnership, association or body corporate and shall be
generally recognised as an expert in the field of cable installation and maintenance. The
independent arbiter shall be mutually agreed between the parties.
The expert shall act on the following basis:
a. on their appointment, the expert shall confirm his neutrality,
independence and the absence of conflicts in determining the
dispute;
b. the expert shall act as an expert and not as an arbitrator;
c. the expert's determination shall (in the absence of manifest
error) be final and binding on the parties and not subject to
appeal;
d. the expert shall decide the procedure to be followed in the
determination in accordance with this agreement and in
consultation with the parties and shall be requested to make his
determination in writing, with reasons, within [30] calendar days
after their appointment.
e. For the avoidance of doubt, all costs related to the instruction the
expert shall be borne equally by the parties.
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10 RECOMMENDED CONSIDERATIONS,
GUIDELINES AND REFERENCES
When planning the route of subsea cables it is recommended that Developers consult the
following International Cable Protection Committee (ICPC) and ESCA Guidelines (these should
be checked for latest versions as they are updated periodically):
Ø ICPC (International Cable Protection Committee) – www.iscpc.org
Ø Recommendation No.1: “Management of Redundant and Out of
Service Cables”
Ø Recommendation No. 2: “Recommended Routing and
Coordinating Criteria for Submarine Telecommunications Cables
in Proximity to Other Such Cables”.
Ø Recommendation No.3: “Criteria to be applied to Proposed
Crossings between Submarine Telecommunications Cables and
Pipeline/Power Cables
Ø Recommendation No.4: “Recommended co-ordination
procedures for repair operations near in service cable systems”
Ø Recommendation No.7: “Procedure to Be Followed Whilst
Offshore Civil Engineering Work Is Undertaken In The Vicinity Of
Active Submarine Cable Systems”
Ø Pipeline Crossing Agreement Template
Ø ESCA (European Subsea Cables Association) Guidelines – www.escaeu.org
Ø DESNZ, 2011. National Policy Statement for Renewable Energy Infrastructure (EN3). [Online]. Available at:
Ø NPS EN-3 - Renewable energy infrastructure (publishing.service.gov.uk)Applying for
safety zones around offshore renewable energy installations
https://www.gov.uk/government/publications/offshore-renewables-energyinstallations-applying-for-safety-zones
Ø Electricity (Offshore Generating Stations) (Safety Zones) (Application Procedures
and Control of Access) Regulations 2007 (SI/2007/1948), Available at:
http://www.legislation.gov.uk/uksi/2007/1948/contents/made
Ø The Crown Estate, 2012. Submarine cables and offshore renewable energy
installations – Proximity Study:
https://www.thecrownestate.co.uk/media/1784/submarine-cables-and-offshorerenewable-energy-installations-proximity-study.pdf
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11 ANNEX A - KEY FACTORS DETERMINING
PROXIMITY DISTANCES
The experience acquired in repairing subsea cables has evolved a recognised set of
maintenance and repair processes and procedures. In order to assist all sectors in
understanding the interactions and impacts, the five key determinants of sea-room required
by a cable ship are summarised in this annex, namely:
Ø
Ø
Ø
Ø
Ø
Fault location;
Cable recovery methodology;
Cable repair methodology;
Repair bight deployment; and
Third party assets location.
In addition, the following basic operating issues governing the determination of proximity
distances are addressed:
Ø Vessel design and capability;
Ø Anchored operations;
Ø Operations within a Hazard Area (or Area of Enhanced
Operational Awareness);
Ø Safety management and competency; and
Ø The role of the Master.
Part of the information contained in this annex is extracted from The Crown Estate’s
Evidentiary Study which contains more in-depth information about the subjects, including
overview tables and worked examples. It is generally recommended to consult this study
report when considering specific issues to be analysed for inclusion in a proximity agreement.
11.1 Fault location
Confirmation of fault location and cable recovery is carried out by ROVs where metocean
conditions allow. For instance the use of electrodes in telecommunication cables fault
finding, trailed behind the repair ship as it zigzags its way along the cable route may however
be necessary for fault location under certain conditions.
Trailed electrodes remain a well proven technique for fault finding in telecoms. It can also be
used to find faults in power cable repair operations; however its utilisation shall be carefully
assessed as per the existent repair scenario details in order to understand whether it will be
successful. For expediency it is common for the main repair vessel to carry out the work, but
auxiliary vessels may also be employed if these are available, and the operational conditions
are suitable.
In either case, the sea-room required for the vessel to safely and efficiently manoeuvre whilst
using trailed electrodes must be properly considered within the proximity agreement.
A typical manoeuvring pattern is illustrated in Figure 12 below.
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Figure 12: The process of determining fault location through the use of trailed electrodes.
(Internal Document, GMSL, 2011)
Electrodes would be approximately 150 m in length in 50 m DOW, and typical distance offline
would be 400-500 m. The latter distance is a function of electrode length, ship length and
requirement to tow the electrodes far enough away from the cable line so that any deflection
is sufficiently positive to inform a judgement on fault location and not be overtly affected by
background noise.
11.2 Cable recovery
The recovery of cables for repair may be undertaken by conventional grappling techniques
(mostly for telecom cables, with its utilisation in power cables needing to be carefully
assessed as per the existent repair scenario) or through the use of a ROV . The sea-room
required to efficiently execute cable recovery is one of the key determinants of cable and
OWF proximity. This should be properly addressed in the drawing up of proximity agreements
and associated documentation.
ROVs & related subsea equipment
In most cases, ROV intervention would be the preferred cable intervention method in deeper
water up to the ROV water depth working parameters, at least initially when the fault location
would be inspected. Once initial ROV inspection has been completed then the options
become broader ranging, including towed grapnels subject to confirmation whether its
utilisation is suitable based on whether the cable is buried, and the vessel equipment can deal
with the tensions generated in the recovering process. The recovery method would be
dictated by seabed type, depth of burial, environmental parameters, cable offline distance (in
which case ROV is preferable), cable type, proximity of hazards, etc.
If these factors allow, once the fault has been located the cable will be exposed, cut by the
ROV and recovered by a lift line, thus reducing the amount of system cable removed and
minimising cable ship excursions from the cable route. Alternatively, the initial cut may be
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performed by ROV before the two cable ends are recovered to deck via grapnels if the
tensions generated during the cable recovery process can be dealt by the vessel equipment.
In some situations, use of ROV may be restricted to initial fault location and identification of
suitable locations to conduct recovery via grapnels only.
Indicative base case proximity distances for ROVs, and other subsea tools can be found in The
Crown Estate’s Evidentiary Study.
Grapnel operations
Grappling is a cable recovery technique mainly for telecommunications cables, especially
when metocean conditions or cable burial preclude the use of ROV. This activity will usually
consist of a cutting drive at the fault position followed by holding drives to recover the two
cable ends. The distance required to conduct both cutting and holding grapnel drives is
broadly similar and is a function of ship length, grapnel rig length, run-on distance (a DOW
dependent distance deemed appropriate to ensure the grapnels have sufficient opportunity
to engage the cable past the cable route before recovery), and layback distance (a distance
to the grapnel rig dependent of DOW , grapnel techniques and vessel speed). Grapnel runs
would preferably be conducted up any substantial seabed gradients and perpendicular to the
cable route, hence they result in the cable ship making significant excursions from the cable
route as in Figure 13 below.
Figure 13: Example of indicative distances required when conducting traditional cable
recovery methods with grapnels in 50 m DOW.
The size of the Working Zone shown in Figure 13 from the cable route may be reduced by
using a shortened grapnel rig layback, conducting operations with the vessel direction parallel
to the cable line or by making optimal use of conditions (further details relating to such a
scenario are provided by The Crown Estate (2012) (refer to Table 0-4 of that Study)). However,
the normal scenario above should be allowed for when discussing proximity and, as grapnel
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operations require more sea-room than ROV cable recovery methods, the use of grapnels is
a key consideration for this Guideline.
Table 1 is offered as a guideline set of base case operational distances for grapnel operations
when considered in alternative to ROV assisted cable recovery. It is acknowledged however
that final proximity distances for a given repair scenario will be dependent on a large number
of variables that combine to produce a unique set of requirements for each cable repair.
Water Depth
(metres)
Layback
(metres)
Run On
(metres)
Length of Grapnel Rope
(metres)
10
30
50
40
20
40
50
50
30
70
50
90
40
100
50
120
50
140
50
150
100
240
50-60
250-300
500
650
200
800
1000
1200
400
1500
1500
1650
500
2200
Table 1 - Indicative reduced grapnel operation distances (also considering The Crown Estate
Proximity Study 2012)
The reduced layback and run on distances provided by The Crown Estate (2012) are to be
considered as ‘shortened’ distances and are derived assuming a reduced grapnel layback. In
practice, an allowance for differences in grappling rig arrangements, operational contingency
(e.g. wind & tidal effects) and attention to the particular circumstances of the case should be
made and the arguments expressed here adjusted accordingly.
11.3 Cable repair
Once a cable end has been recovered and “recovery” damage removed, the system is tested
to determine whether the end is faulty or fault free. If faulty the vessel will proceed to clear
the fault . Once the cable has been cut back sufficiently to remove the fault and has been
tested successfully the cable ship will buoy off the good end and relocate to recover the other
side of the cable.
The cable ship will repeat the process on the second end until it is standing to a fault free end
and will then splice to a length of repair “stock” cable. Once this splice is completed and
tested, the cable ship pays out the new “stock” cable section (depending upon the position
of the cable ends during fault location, the cable ship will aim to place the cable on the original
cable route) laying out to the first cable end buoy – including any crossing constructions which
may be required over inter-array or export cables.
When the cable ship reaches the cable buoy it will recover the first end, test both ends and
perform the final splice (see Figure 14 below).
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Figure 14: The repair of a cable is usually not dimensioned in respect of proximity distance
to a wind farm structure
11.4 Repair bight deployment
Once the final repair joint is complete the vessel will manoeuvre to lay the final bight, as in
Figure 15, and, if possible, the entire repair footprint will be re-buried using the ROV.
It should be noted that the physical characteristics of the repair bight are dictated by the
variations in design and purpose of the vessel involved.
Figure 15: Example of indicative distances displaced off the cable line when deploying a final
bight to the seabed in 50 m DOW.
The displacement of a final bight created by a cable repair will be a function of:
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Ø water depth;
Ø the physical characteristics of the cable, particularly bend radius
and catenary;
Ø deck length, jointing space layout and freeboard of the cable
repair vessel; and
Ø prevailing weather conditions at the time of the laydown
operation.
Figure 16 illustrates the terms ‘water depth’, ‘freeboard’, ‘deck length’ and ‘repair bight
crown’.
Figure 16: Terms relating to cable repair bights
The deployment of a final bight is likely to be the key determinant of the space required to
conduct maintenance of a subsea cable in the vicinity of an OWF development. Not only is it
likely that the operation during a repair requires the greatest excursion offline, hence placing
the vessel closer to the OWF than at any other stage of the repair operation, it takes place
when the cable ship is least manoeuvrable and most constrained in her ability to respond to
any loss of position. A method to reduce the risk of the proximity of the ship and the nearest
WTG structure is to plan the deployment of the final bight between or away from the WTG if
achievable. If practicable, the ROV will also be utilised to inspect and re-bury the cable post
repair. Attention is drawn to the differences in bight deployment techniques between
telecoms and power cables. Also, the differences in preparation and laying out of cable ends
for jointing are significant when comparing telecoms and power systems. As such, due
recognition of each should be fully incorporated in all proximity planning.
11.5 OWF foundation type and design
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OWF’s use different types of foundation, and these can have some influence on the cable
proximity distances. Early OWF’s have predominantly adopted fixed foundations using
monopoles, mini jackets and some gravity base foundations.
These types of WTG designs are connected by static cables laid on the seabed up to the
foundations. The foundations themselves are not typically a part of the key considerations for
proximity as their seabed footprints are normally smaller than the WTG blade diameters or
do not extend far beyond the surface footprint of the structure. They are therefore generally
not a critical factor for proximity.
Floating OWF Developers are considering a variety of foundation designs including semisubmersible, spar barge and tension leg platform designs. Some of these use anchors and
mooring lines extending from the floater and the lengths and designs for these depend on the
water depths and shallow soils.
Figure 17: Examples of foundations design (Image courtesy of ORE Catapult – UK Floating
Offshore Wind Centre of Excellence)
These FWTG foundation designs are connected by dynamic power cables which can feature
buoyancy modules and often have cable catenaries which extend away from the floater.
Because of this, floating OWF foundations and in particular their moorings are more critical
to proximity calculations and are the key part of OWF infrastructure to be considered rather
than the WTG itself. Mooring systems are broadly grouped into two categories: catenary and
taut systems.
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For more information concerning floating OWF design, as an example there is information
available in the Floating Offshore Wind Technology and Operations Review Document from
ORE Catapult – UK Floating Offshore Wind Centre of Excellence.3
11.6 Vessel design and capability
It is demonstrable that with increasing technical reliability of propulsion and control systems,
the main causes of DP station keeping incidents are related to human error. While the DP
class of a particular vessel remains relevant, procedural regimes and behavioural safety are
of significant importance in developing proximity distances for DP and other self-propelled
vessels.
When drafting a proximity agreement on which a telecommunications cable is involved, it
must be recognised that DP class 1 vessels are commonly used for telecommunications cable
repair, providing lower levels of redundancy in the event of a system failure or loss of position.
Proper operating controls and procedures shall be followed. The use of DP class 1 vessels
should not translate into more station-keeping incidents than for DP class 2 vessels on the
assumption that DP class 1 vessels are operated more conservatively in terms of proximity
distances.
11.7 Anchored operations
An anchored barge may be used for cable installation or repairs in proximity to an OWF or
conversely for OWF work in proximity to an existing cable. For floating OWF’s special
attention needs to be taken concerning the anchored barge mooring and the floating wind
structure mooring system. The use of jack up barges for OWF construction or cable repair
activities can also involve the deployment of anchors to aid positioning prior to jacking
operations.
While the deployment of anchors represents an additional constraint when planning
proximity distances, the fact that anchor lines can span an existing subsea cable allows a
degree of flexibility in the use of anchors in a congested seabed area.
While it is not possible to prescribe minimum proximity distances for anchors and wires that
suit all situations, given proper controls, some base case limits for anchored operations can
be found in The Crown Estate’s Evidentiary Study.
The proximity and direction of anchors should be given specific consideration and procedural
process in the site proximity agreement.
11.8 Safety management and competency
The station keeping performance capability of any vessel is a combination of design,
maintenance standards and operational competence in the face of environmental and sitespecific conditions. This Guideline considers that close attention to safe operating practices,
competency assurance and behavioural based safety should be equally important as the
3
https://ore.catapult.org.uk/?orecatapultreports=floating-offshore-wind-technology-operations-review
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technical reliability and performance of vessels and equipment when defining proximity
distances.
Whilst the safe operation of vessels is legislated at international and national levels, there are
a range of applicable safety standards depending on the size and/or power of a particular
vessel. Some vessels (particularly towed barges) fall outside the more stringent requirements
such as the International Safety Management (ISM) Code. It is recommended that the
principles of the ISM Code be applied to proximate vessel operations irrespective of vessel
size, power or class.
11.9 Operations within a notification area
Typical crossing and proximity agreements generally prescribe additional safety controls
within a defined area around a fixed or floating structure to manage the additional safety
hazards present. A ‘notification area’ around structures is often adopted where vessel entry
would activate these additional requirements specified in the crossing or proximity
agreement. It is recommended that the definition of such a notification area be included
within the proximity agreement within which a heightened level of operational readiness and
safety awareness be activated.
11.10
The role of the Master
In common with conventional maritime law and practice, the ship’s Master has overall legal
responsibility for the safety of his vessel, the personnel on-board, and the protection of the
environment. It is recommended that this is properly acknowledged in the development and
spirit of the proximity guidelines and that nothing contained therein should detract from this
ultimate responsibility for the safe conduct of operations.
It should be noted, the prerogative of the vessel’s Master will play a significant part in the
actual execution of the works that are defined within any proximity agreement and in all
vessel operations discussed therein. This Guideline considers it imperative that maintenance
suppliers and their marine personnel (of both parties) be engaged in both the proximity
agreement formulation and any repair operation planning.
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12 ANNEX B STAKEHOLDER CONSULTATION
This annex describes a typical offshore wind development programme and the sequence of
high-level activities and proposed Stakeholder interactions during the various project phases.
The TWG acknowledges that some OWF Developers may choose to progress further with
proximity agreements, prior to consent application, than suggested below. However, Figure
18 below, and the explanatory text, provides some guidance on the suggested timings of
interactions between an OWF Developer and subsea cable operator.
Figure 18: Suggested Stakeholder consultation during development and construction of an
OWF project
12.1 Development and consenting phase
In the UK the processing model for OWF’s can take more than 5 years from identification of a
development zone through to commencing construction. Developers have several stages to
complete before gaining planning consent. Owing to the nature of the planning system for
offshore renewable energy projects, detailed and effective engagement is required with all
Stakeholders during this time and the Developer must report on this consultation and on the
way in which Stakeholder concerns have been considered within their consent application.
The processing model for OWF’s in other countries in geographic Europe can be included in
this Guideline as an annex in future updates.
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The first liaison activities between the Developer and the involved Stakeholders should
include advice on intent, process and timescales of the development.
Communication should include the issue of charts providing details of the site under
development. Where possible, this could also be provided in a suitable GIS format. Once
communications have started, follow-up communication should continue on a regular basis –
perhaps twice a year (although this should be agreed on a case-by-case basis, depending on
the potential nature of the interaction between parties).
Once a project (or zone development plan) is better defined, one-to-one meetings with the
affected Stakeholders should commence. The key aim of these meetings should be to discuss
proximity issues and the potential requirements for cable crossings. Under the Planning Act
a Developer must demonstrate a suitable level of consultation and engagement with a
project’s Stakeholders. As a result it would also be beneficial to discuss the overall nature of
the principles which will need to be established between the two parties when coming to
proximity or crossing agreements.
It should be noted that even at the point of consent application, the OWF Developer may not
know the exact layout of the OWF. In the UK OWF’s are usually consented on a ‘project
envelope’ basis, known as a Rochdale Envelope, which allows for a variety of potential options
in technology, layouts, project size, etc to be built out. Importantly for this document, the
layouts are only likely to be confirmed post-consent. Whilst some Developers will be happy
to sign up to certain distances on which a proximity agreement can be reached before
consent, it may not be possible to sign full proximity and crossing agreements before the
submission of a consent application if Developers cannot provide this level of certainty. It is
therefore anticipated that where Developers cannot sign up to certain constraints before
consent application and hence where there are potential conflicts between a cable and an
OWF proposal (and where there is a possibility that the cable operator may object to the
planning authority as a result of the conflict) the affected parties may look to develop a twostage agreement. The suggested stages for this are detailed below but may need to be
adapted to meet the needs of individual Developers and their Stakeholders.
Whilst an OWF Developer, in this instance, would not be able to provide final details of a
project layout pre application, it is suggested that parties consider entering a high-level
Memorandum of Understanding (MOU) before a Developer submits a consent application to
avoid the need for any objection to an application. The level of information within this MOU
would be largely dependent on the desired level of agreement, pre-consent, of the OWF
Developer and cable owner. It is suggested that such a high-level MOU would look to establish
the principles on which a proximity agreement would be reached for the project in question
and would intend to focus the parties on the principles laid out within it.
Such a high-level MOU may look to identify minimum proximity without any compromise to
maintenance operations on the telecoms operator’s part as well as, for example, suggesting
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suitable mitigation measures that could be adopted should proximity be reduced in a number
of increments. This may present numerous scenarios on which the OWF Developer could
base a design when finalising the OWF design depending on the final project parameters,
hence retaining the flexibility contained within the Rochdale Envelope.
It is recognised however that an MOU may not be applicable or appropriate for all Developers
and hence it is suggested here as one option to ease concerns of both parties. A Developer
(or existing cable owner) may prefer to take another approach as part of ongoing consultation
on the proximity agreement.
During the discussions on a high-level MOU, the parties may agree to undertake certain
impact assessment analyses and technical studies, if required, to determine the level of risk
imposed and allow an informed discussion of potential mitigations.
If considered appropriate, a high-level MOU would be put in place between the Developer
and the affected party as part of the consultation process. In this case, it would provide the
OWF Developer and affected party with the reassurance that a project will proceed on the
previously agreed terms and hence will avoid potential further dispute at a later stage.
In this scenario, the second stage of the proximity agreement would occur post-consent and
once the layout has been approved, where detailed agreements between cable operators and
OWF Developers are finalised and agreed (as discussed further in Annex B.3).
12.2 Pre-construction phase
Once consent is granted by the relevant authority, the Developer will start narrowing down
design options for the OWF through detailed design, tendering and procurement processes
(although some Developers may begin this process during application determination). During
this period (typically approximately 2 years), the Developer should continue to engage with
the cable owners and establish more firm proximity (and crossing) agreements in line with
the previously agreed principles laid out within the high-level MOU or any other applicable
documents. These would be based on the established OWF layout, electrical infrastructure,
etc.
Depending on the nature of the OWF consent, there may also be a requirement to
demonstrate to the regulator that a proximity agreement has been reached.
12.3 Construction phase
Once the financial investment decision is taken by the Developer’s board(s) and offshore
construction is mobilised, there will be certain precautions to be taken in respect of
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construction operations near offshore cables. This is detailed in the method statement
forming an integral part of any proximity agreement.
Representatives of installation and/or maintenance contractors should be involved in
operational discussions as early as possible, as necessary. This is to enable agreement of
working arrangements for installation, repair and maintenance of the parties’ facilities within
the bounds of the proximity (and crossing) agreement.
Notification for defined activities should be provided as agreed on a case-by-case basis. An
example of a notification timeline could be at countdown intervals of 3 months, 1 month, 1
week, 48 hours, 24 hours prior to construction commencement and upon completion of
operations. Any alterations to the Method Of Procedure (MOP) during construction will
require further discussion and flexibility in the proximity agreement.
12.4 Operation and maintenance phase
Following construction, the coordinates and necessary charting information shall be supplied
to all parties as soon as practical to enable them to update their databases. The obligation is
to provide as-built data works for all parties. The OWF operator should provide as-built data
and as-laid coordinates of all infrastructure. Subsea cable operators should provide a revised
route position list after a cable has been lifted for repair or installation of a new cable.
During the operation and maintenance phase there will be new issues in respect of marine
coordination, issues during major overhauls, etc., and there might be options for shared
maintenance services.
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13 ANNEX C – CHECK LIST FOR ISSUES TO BE
CONSIDERED IN A SITE-SPECIFIC RISK
ASSESSMENT
This annex provides a check list of the key issues (‘external/internal influences’) for
consideration in a site-specific risk assessment. It may be appropriate to consider these as
part of a suggested agenda for discussion between the key Stakeholders.
Site specific proximity
distances
Figure 19 – The external and internal influences to be considered in determining site specific
proximity distances
13.1 External influences
The following is an aide-memoire of the key areas of ‘external influences’ (i.e. issues where
none of the affected parties can have an impact on the condition) for consideration in
reaching successful proximity agreements. It is not intended to be an exhaustive list of items
to be included by prescription.
Physical environment/metocean conditions
Ø Historical metocean data;
Ø Benthic conditions;
Ø Depth of water (DOW).
Existing infrastructure
Ø Availability of accurate survey data;
Ø Existing subsea plant information (burial/protection) and
specification;
Ø Other seabed users/Stakeholders and proximate Developments;
Ø Cable crossings and any required burial/protection (mattresses,
rock etc.);
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Ø Proximity of surrounding infrastructure foundations/WTG’s/
substations.
Planned infrastructure
Ø Planned location and potential layout scenarios, including
crossings.
Legislative/regulatory constraints
Ø
Ø
Ø
Ø
UNCLOS and other regulatory constraints;
HSE regulations;
Local rules and regulations;
Other permit applications lodged during development of a
proximity agreement.
Commercial constraints
Ø Is a high-level MOU between the parties in place?;
Ø Impact on contractual performance requirements of cable
owner’s customers/marine provider;
Ø Reduction in OWF Developer’s power generation.
Other seabed users
When subsea cables are located in close proximity to OWF Developments and other
Stakeholders (such as oil & gas, shipping, aggregate extraction, marine protected areas, etc.),
the Developer should consider the cumulative impact of all the sectors’ requirements. This
should ensure each Stakeholder can continue their legitimate activities in a safe and timely
manner. Where impacts are identified, they should be quantified and assessed, and all
legitimate concerns addressed. Where multiple developments/Stakeholders are identified,
the Working Zone agreed between Stakeholders using this Guideline may vary on a case-bycase basis.
13.2 Internal influences
In addition to the external influences outlined above, a range of ‘internal influences’ (i.e.
issues that are in some kind of control by at least one of the affected parties) should also be
taken into consideration when discussing a risk-based assessment of appropriate proximity
distances. Again, the list is not intended to be exhaustive or prescriptive but should prompt
evaluation of the most useful and relevant issues for consideration.
Also, these internal influences should be part of the agenda for discussion between the key
Stakeholders and may eventually be elements of the method statements to be developed and
agreed through the dialogue.
Vessel/equipment selection or availability
Ø
Ø
Ø
Ø
Differing vessel types, capabilities and operating footprints;
Vessel and positioning capability;
Weather forecast and related decision process;
Impact of vessel losing position;
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Ø Vessels required to undertake remedial works–multi-vessel
simultaneous operations;
Ø Position reference systems and the impact of surrounding
structures;
Ø Deck and cable handling arrangements;
Ø ROV/LARS spec and capability;
Ø Methodology, operational procedures and techniques
employed, including SIMOPS (Simultaneous Operations
Procedures);
Ø Available spare cable/plant.
Operational environment
Ø Proximity agreement boundary;
Ø Pre-existing jack up zones and cable-free areas;
Ø Anchor spread requirements for multi-point mooring systems
including floating OWF mooring systems;
Ø Cable protection;
Ø Post-lay surveys and the transmitting /sharing of data;
Ø How a repair affects future interaction and works;
Ø The requirement for powering down part of a system during
works.
Manning levels
Ø Competence and experience adequate to meet the additional
demands of the circumstance;
Ø Additional manning requirements, e.g. DPOs, watch keepers,
proximate party reps, operational personnel to expedite the
repair, etc.
Personnel competency
Ø Ensure that relevant cross sector expertise is engaged;
Ø Health, Safety and Environmental considerations;
Ø Experience in proximate/close quarters/simultaneous
operations.
13.3 Application of ALARP
What is ALARP?
The ALARP level should not be misunderstood as simply being a quantitative measure of
benefit against detriment. ALARP is reached when the time, trouble and cost of further
reduction measures, become uneconomic or unacceptable with respect to the additional risk
reduction obtained.
In order to come to an agreement between the involved parties it will be necessary to
determine the level of risk ALARP level which is acceptable to each Stakeholder. This will be
site specific and the appetite for risk is likely to vary.
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Whilst account should be given to potential worst case scenarios, these should not be used
as the basis for discussions between the parties if they cannot also be considered likely.
Limiting discussions to worst case scenarios or, for instance, a single 20 year + event, is likely
to lead to disagreements where neither party can be satisfied or may potentially prevent an
agreement being reached at all. Wherever possible, the assessment of risk should include,
but not be limited to:
Ø Any historic data available on reliability or damage for the
existing infrastructure or installed similar examples elsewhere;
Ø Likely return rates of periods of poor weather which may, under
the planned interaction, prejudice repairs when compared to the
baseline current situation;
Ø Likelihood of inability to maintain control of the vessel; and
Ø Completion of sufficient due diligence to ensure that all parties
to the agreement are considered competent to meet the
requirements of the proximity agreement.
Consideration of the acceptable risks will then allow informed discussions on the potential
mitigations that may be available to reduce the risk caused by a new development and
therefore reach an acceptable ALARP level.
Consider the following ‘probability impact (P-I) table’ and ‘risk severity analysis’ example
when determining and mitigating to the ALARP (YELLOW) level(s). Note, the risk severity index
can be calculated simply as Probability x Highest Impact, the solution being inserted within
the P-I table in the green (tolerable), yellow (ALARP) or red (intolerable) areas.
This might be viewed in a probability impact (P-I) severity table as outlined in Figure 20 below.
Highest impact of risk event
Figure 20: Probability impact table and associated ALARP levels
A risk analysis taking into consideration all site-specific external influences and internal
influences should be carried out during discussions on proximity agreements. The base case
proximity distance tables provided in the Evidentiary Study (The Crown Estate 2011) applied
intelligently provides useful tools in the risk assessment of the various scenarios.
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Such an assessment could include but not be limited to:
Ø Risk/likelihood of damage to existing/proposed infrastructure in
the area of the interaction including potential for change to
anticipated fault rates due to the planned new infrastructure;
Ø Risk/likelihood that a fault may occur during a period of poor
weather which would lead the Master of the vessel to delay or
suspend operations due to the proximity of an OWF alone (as
opposed to the weather being unworkable in any situation);
Ø Acceptable level of downtime of any infrastructure under
normal circumstances and its strategic importance;
Ø Loss of potential revenue for any OWF operator as a result of loss
of available acreage and impact on the project as a whole;
Ø Cost of alternative options, such as, re-routeing a new cable
around as opposed to through an existing OWF and impact on
the project as a whole.
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